The "baz" was a kind of "bass saz", made by sticking a cello fretboard, bridge and strings (salvaged from a local skip!) onto an old saz - surprisingly effective as an acoustic bass.
Lady Chapel, Glastonbury Abbey
The schottische is allegedly one by Jonathon Shoreland (Fernhill, Primaeval). Cliff Stapleton (Blowzabella, Primaeval) wrote "Boys of the Mill". "Constantine" is a Cornish funeral hymn. "Cochon Chine" was described by Joel as "an awful Saint-Chartier standard" - some kind of novelty 3-person schottische-type dance - here being played as a joke (but quite a good version).
A little bit of splicing and EQ has been used to improve the overall sound.
Abbey ruins in Avalonian mist, geometric plan of the Lady Chapel
The geometry of the Abbey, particularly the Lady Chapel is fascinating, and has been explored by writers such as John Michell. This chapel is the supposed site of the first Christian Church built in the British Isles, built, according to legend, by Joseph of Arimathea. Here is an introductory website.
Some more recordings from the Lady Chapel can be found here.